The 3rd Generation Partnership Project (3GPP) standard defines procedures for user equipment (UE) to handle multiple incoming calls in particular scenarios. One scenario involves receiving a second call at a terminating UE while a first call previously received by the terminating UE is still being setup. In this scenario, the 3GPP standard defines a “first come, first served” approach for handling the second call during the setup of the first call. Following the first come, first served approach, when the second call is received during the setup of the first call, the terminating UE rejects the second call and attempts to finish the setup of the first call. This is a fair and sensible approach if the second call was truly originated by a different calling party than the calling party that originated the first, initial call.
However, it is often the case that the same calling party originated both the first and second calls. This can occur for various reasons, but perhaps most often, the second call is “re-attempted” via a different call path (e.g., using circuit switched (CS) fallback procedures) because of an issue that arose while attempting to establish the first call via an initial call path (e.g., poor radio coverage using a preferred network). In this example scenario, the originating UE may request to terminate the session setup of the first call by sending a Session Initiation Protocol (SIP) message using the SIP CANCEL method. Sending SIP CANCEL message from the originating UE is a best effort procedure that is not guaranteed to successfully terminate the setup of the first call because the SIP CANCEL message can be lost due to the same problems (e.g., poor radio coverage) that caused the issue with establishing the first call in the first place. Accordingly, before receiving a CANCEL response at the originating UE, the originating UE can send a second session request via the legacy (CS) network as part of the CS fallback procedure. Because automated re-attempt procedures, such as CS fallback, occur vary rapidly, a second call from the same calling party can be received by the terminating UE within a relatively short time period (e.g., within about 5 to 20 seconds) from the time a first call was received, and, when the second call is received, the setup procedures for the first call may still be ongoing. In this scenario, the first come, first served approach can be detrimental to successful call establishment because the second call—despite often having a higher chance of success than the first call—is rejected by the terminating UE in preference of finishing the setup procedures for the first call. If establishment of the first call fails, the parties to the would-be communication session are not connected, resulting in a poor call experience.